Learning About Tests for Latent Tuberculosis (TB) in Children

What are they?

Your child may have tests to find out if your child has latent tuberculosis (TB). Children with latent TB have the TB bacteria in their bodies. But they don't have any symptoms of TB. The tests may include the tuberculin skin test or the interferon-gamma release assay (IGRA) blood test.

Why are these tests done?

If your child has been in close contact with someone who has TB, your child could be infected. Tests help your doctor find a latent (inactive) TB infection. Then your child can get treatment if needed. This can prevent latent TB from becoming active TB disease that can spread to other people.

How do you prepare for the test?

If the doctor suggests a TB skin test for your child, tell the doctor if your child has had the BCG vaccine. It interferes with skin test results. People who get the BCG vaccine are likely to have TB test results that show they have a TB infection even when they don't.

How are these tests done?

Your child may get the tuberculin skin test or the interferon-gamma release assay (IGRA) blood test. The skin test is often used in children younger than 5 years old.

During the skin test, part of a TB bacterium is injected under your child's skin. The test feels like a quick needle poke.

For the blood test, your child's blood is taken by a health professional. It is then tested in a lab.

What happens after the test?

Your child must see the doctor again 2 to 3 days after the test to have the skin test checked. If your child has TB in their body, a firm red bump will form at the shot site within 2 days.

The doctor may want to repeat the skin or blood test again in several weeks.

If the tests show that your child is infected with TB, the doctor may order more tests. These may include checking the mucus in your child's lungs or taking an X-ray. They can help the doctor find out if your child has active TB disease that can spread to other people.

The test results will help the doctor decide on any treatment.